The UK's "complex agenda" is preventing it from doing more to ensure the arrest of the Sudanese president, Omar al-Bashir, for war crimes and crimes against humanity, the world's most powerful prosecutor said yesterday, claiming that Bashir "continues to commit crimes every day".

Speaking at the Hay literary festival, the chief prosecutor of the international criminal court, Luis Moreno-Ocampo, below, singled out the UK as one of a number of permanent members of the UN security council that should show "unity and leadership" in taking a tough line on Sudan.

"Bashir must be stopped," he said. "The destiny of Bashir is to face justice – it's a matter of time. If China, the US, the UK and Europe acted together, we would stop him". But he added: "What's the advantage for UK to be tough with Sudan when they have so much else on the agenda?"

Moreno-Ocampo's comments come as opinion on the Sudanese president's indictment continues to be divided. The prosecutor called for his arrest in July last year, accusing Bashir of orchestrating a campaign of killings, rape and deportation in the western region of Darfur.

A number of African and Arab countries, as well as NGOs working in Darfur, have criticised the decision to indict Bashir, claiming it has jeopardised the Darfur peace process in Doha, Qatar.

The peace talks have seen a flurry of diplomatic activity in recent days. US officials have travelled to China and plan to meet British, French and Russian diplomats to try to end the six-year war between the Arab government in Khartoum and ethnic minority rebels in Darfur.

A hybrid peacekeeping force was established in Darfur in July 2007 under a coalition between the UN and the African Union. With an estimated strength of 26,000 troops, it is expected to become the largest peacekeeping force in the world.

But critics, who say the peace process has been hampered by a lack of co-operation from the Sudanese government, claim that Moreno-Ocampo's decision to call for Bashir's arrest will further compromise the chances of peace in the region.

The comments are the latest development in a long-running series of controversies involving Moreno-Ocampo since he was appointed as the ICC chief prosecutor in 2003. Although respected by many for his record in prosecuting military generals in his native Argentina, he drew widespread criticism for his initial decision to request Bashir's arrest for the crime of genocide.

The charge was later dropped, leaving Bashir charged with counts of war crimes and crimes against humanity.

Moreno-Ocampo also attracted criticism for his conduct of a case in which an ICC staff member accused him of sexual misconduct. Although the allegation of sexual misconduct was later discredited, critics called for the prosecutor's resignation after he dismissed the staff member in what was later described as a "breach of due process".

Moreno-Ocampo's talk at the Guardian-sponsored festival in Hay-on-Wye was the first time he had spoken in the UK in such open terms about his role as the world's first criminal prosecutor.

His interview, with international law expert Phillipe Sands, was one of a number of high profile political and legal discussions raising issues on civil liberties and freedom of speech.

Sources in the Foreign Office said they were surprised by Moreno-Ocampo's apparent criticism of UK foreign policy. The UK has supported the independence of the ICC and so far resisted calls by some African and Arab leaders for the warrant for Bashir's arrest to be deferred.

However Britain, along with other permanent UN security council members the US and France, has supported the current Doha peace process and is currently attempting to broker a deal between rebel leaders and the Sudanese government, with the possibility of deferring the indictment against Bashir.

Moreno-Ocampo also drew criticism for announcing in advance his request for a warrant to arrest Bashir, which some critics say alerted the Sudanese president to the possibility of his arrest, leading him to avoid travel to countries which had signed up to the international criminal court.